The invention is based on a fuel injection nozzle for internal combustion engines which has a valve needle stressed by a closing spring and urged in the opening direction by fuel pressure; the valve needle is coupled with a damping device, which during the opening stroke damps the movement of the valve needle in accordance with at least one operating parameter of the engine but is ineffective during the closing stroke. The damping device serves to control the opening cross section of the injection nozzle such that the various demands on the engine at various rpm and loads are met.
Such damping devices are known both for injection nozzles with valve needles opening in the flow direction of the fuel (A-type nozzle) and for those having valve needles opening inwardly (I-type nozzle). In the known injection nozzles, the damping is adapted such that the return action of the damping means, for instance a body having mass, is made complete at every rpm and load point of the engine, and the subsequent opening movement of the valve needle is effected in a damped manner either from the outset or beyond a fixed, predetermined, short pre-stroke. The result of this damping characteristic can be that at higher engine speeds and higher loads, the duration of injection is excessively long.
In order to overcome this disadvantage, it has already been proposed that the damping be made effective even before the end of the opening stroke of the valve needle (German Offenlegungsschrift No. 32 02 364.2). This disclosure provides for a considerable shortening of the total duration of an injection process to be attained.
In spite of these efforts, the problem still exists that the instant when the damping becomes ineffective is fixed in accordance with the needle stroke, and so certain compromises must necessarily be made between idling and full load of the engine.